AM1-SM2 Calculations Model the Redox Potential of Nitroxyl Radicals Such as TEMPO

Abstract

Nitroxyl radicals can be oxidized to N-oxo ammonium salts that are themselves useful oxidants for primary and secondary alcohols. Several computational methods were investigated in order to predict the redox potential of nitroxyl radicals and to better understand the behavior of different nitroxides as catalysts for alcohol oxidation. The difference in calculated heats of formation for N-oxo ammonium ions and nitroxyl radicals using AM1 did not lead to a useful correlation with experimental redox potential as measured by cyclic voltammetry. However, when both the N-oxo ammonium ion and the nitroxyl radical were evaluated using the Cramer-Truhlar solvation model (SM2), a linear correlation was observed between the difference in heats of formation and the experimental redox values. This correlation may be used to correctly predict the redox potential of new nitroxyl radicals.

Redox-Induced Aromatic C–H Bond Functionalization in Metal Complex Catalysis from the Electrochemical Point of View

“…However, the failure of the reaction in the presence of TEMPO can be explained; the latter is easily oxidized itself by the applied oxidant PhI(OAc) 2 (Table 2). Moreover, if TEMPO was taken in two-fold excess over the oxidant, the entire oxidant was consumed by the side reaction of TEMPO oxidation, which is easily oxidized to about 0 V [60,61], but not by the oxidation of more difficultly oxidized palladacycles. It is known that oxammonium salts are effective oxidant species derived from TEMPO [79].…”

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

“…However, none of these nitroxides outperforms TEMPO and its derivatives. Rychnovsky et al 18 measured the redox potentials of oxammonium salts formed from cyclic nitroxides, using cyclic voltammetry, whereas Suemmermann and Deffner 109 measured those of acyclic nitroxides. There are also examples of oxidations carried out with oxammonium salts formed electrochemically.…”

“…Ali and Wazeer 178 and others 179 have shown that oxammonium compounds are intermediates in the preparation of nitrones by the oxidation of the corresponding hydroxylamines. Rychnovsky et al 18 showed that TEMPO can be oxidized to the corresponding oxammonium and reduced to the corresponding hydroxylamine anion electrochemically. This is the common pattern observed with bisneopentyl nitroxides in which the corresponding oxammonium cannot undergo tautomerization.…”

“…As a control, the cyclic voltammogram (CV) of TEMPO was first recorded with a procedure based on the protocol of Rychnovsky et al 18 The CV of TIPNO was recorded (Fig. 3).…”

“…These unusual properties have led to a wide range of applications spanning their use in biology as spin labels [1][2][3][4][5][6] to the development of organomagnetic materials. 7 In organic chemistry, nitroxides have been used in kinetic studies, [8][9][10][11] as oxidizing species in the form of the corresponding N-oxo ammonium salts, [12][13][14][15][16][17][18][19][20][21][22][23] as temporary caps for transient carbon radicals, [24][25][26][27][28][29][30][31] and as probes for stereocontrol with prochiral carbon radicals. [32][33][34][35][36] In polymer chemistry, nitroxide-mediated polymerization (NMP) [37][38][39][40][41][42][43][44][45][46][47] has become popular as a method for preparing living polymers ...…”